This invention relates generally to a contact lens with improved eye-compatibility. Contact lenses usually are made of inert, non-toxic, optically clear, and schlieren-free plastic materials. The contact lens material may be hard contact lens material, e.g. polymethyl methacrylate, or else soft contact lens material, e.g., polyhydroxy ethylmethacrylate, or polyethylene glycoldimethacrylate. Thin contact lenses made of gas-permeable polymers are preferably in use at this time as they minimize the effect on the metabolism of the underlying cornea. The selection of suitable polymers or subsequent surface treatment renders the contact lenses wettable by aqueous solutions.
The main problems of wearing contact lenses are:
mechanical irritation of eyelid and cornea,
contamination, cleaning, and disinfection of the contact lens; and
reduction of tear-film stability.
Depending on the type of contact lens, a wearer can get used to the mechanical irritation within a period ranging from a few hours to no more than weeks.
The second problem, contamination of the contact lens by non-specific adsorption of lipids, proteins, mucins, and salts of the tear-film as well as by other molecules and particles, including microorganisms, is commonly taken care of by regular cleaning and disinfection. Detergents, as well as proteolytic enzymes, are used for cleaning the contact lens. Proteins that are not removed completely from the contact lens frequently are denatured during cleaning and chemical or heat disinfection and can cause allergic reactions in the conjuctiva of the contact-lens wearer.
As for the third problem, reduction of tear-film stability, it helps to understand the structure of the tear film. The human ocular tear film consists--in simplified presentation--of three layers:
a mucin layer that smoothes the rough surface of the corneal epithelium and renders the hydrophobic corneal epithelium wettable;
an aqueous phase; and
a lipid layer that insulates the aqueous phase from the surrounding air.
The lipid layer of the tear film prevents rapid evaporation of the aqueous phase and excessively rapid cooling of the cornea. The wearing of conventional contact lenses causes a reduction of the stability of the tear film and consequently a more rapid evaporation of the aqueous phase of the tear film. For that reason, contact lens wearers frequently suffer from dry eyes and often must resort to eye drops to relieve the problem. Moreover, the instability of the tear film leads, in many cases, to non-tolerance of the contact lens.